It has also been signed by Jill Gant, the mother of Mark Wood, a disabled man who starved to death in 2013 after he was found “fit for work” through the work capability assessment (WCA) system, and lost his out-of-work disability benefits.

The party has compiled a dossier of this and 49 other deaths of benefit claimants where, it says in the letter, there is “good reason to believe their treatment at the hands of your department has been a factor in their deaths”.

The Green Party letter says the inquiry should examine “the methods used to assess claimants and their entitlements” and “determine whether these procedures are fair and proper or if they are, in fact, contributing to the deaths of some of the claimants”.

The letter points out to Damian Green that, in many of the cases included in the dossier, coroners have “expressed grave concern about the methods employed by your department”.

It adds: “The more time passes without an inquiry, the longer concerns will remain and questions will hang over the procedures used by your department to handle benefits.”

Bartley told DNS yesterday (Wednesday) that he supports attempts to bring a criminal prosecution against former work and pensions ministers Iain Duncan Smith and Chris Grayling over their failure to address the safety of the WCA.

They were warned by a coroner in 2010 to review the policy not to seek further medical evidence from the GPs and psychiatrists of claimants with mental health conditions, but they failed to respond to the report, and apparently failed to pass it on to the expert they commissioned to review the WCA.

As a result of their failure to act, claimants with experience of mental distress continued to die, including Mark Wood.

Bartley said: “I think there are very good grounds for it. If there was criminal negligence in the workplace that resulted in deaths, you wouldn’t think twice about it being right to prosecute.

“I think it’s something we should be supporting. I would be very keen to talk to a lawyer who would be interested in taking this forward.”

He said there was still much that was not known about what ministers knew, and when, about the WCA scandal, but he added: “I think the more evidence emerges, the more we realise quite how aware they were of it and the stronger the case becomes against them.”

Bartley said: “We are supposed to be a civilised country and we are supposed to judge our country by the way it looks after those who are marginalised and disabled.

“It’s absolutely damning that this should be happening in a country that is so rich.”

He said the dossier was “putting down a marker that these rights that have been fought for are being eroded, and not just eroded, but being pushed back, and ground is being lost that has been won over many, many years.

“We have to learn the lessons of history: that things can move backwards as well as forwards.”

Bartley said that “too much ground” had been conceded by mainstream politicians to right-wing ideologies that play on the “mantra of deserving and undeserving [benefit claimants], and demonisation of disabled people and scapegoating of disabled people and that idea of [claimants] being guilty until proven innocent”.

The inquiry call has been backed by DPAC, whose work on benefit-related deaths and other harm caused by the government’s social security reforms triggered an inquiry by the UN’s committee on the rights of persons with disabilities, which found “grave or systematic violations” of disabled people’s rights.

Linda Burnip, co-founder of DPAC, said: “As the UK government has been found guilty by the UN of committing grave and systematic violations of disabled people’s human rights, we feel a public inquiry into deaths which have been linked to the discredited work capability assessment regime must urgently be initiated by the government and the Department for Work and Pensions (DWP).”

A DWP spokeswoman said: “The department will respond to the letter once it has been received.

“We constantly review our processes and procedures and have made significant improvements to the WCA since it was first introduced in 2008, particularly for people with mental health problems, following a number of… reviews, including five independent ones.

“There will also shortly be a second independent review of personal independence payment since it was introduced in 2013.

“And, as you know, we carry out peer reviews to help staff to continually improve how they deal with some of the most complex and challenging cases.”